Draft angle and undercut analyses
In the 3D printing game it would be called the 'self-support angle'.

This setup assumes that the upside of your STL/mesh is oriented in the +Z direction.



The example is targeted at a 3D printer which behaves as follows:


prints perfectly up to 30 degree angle (white colour)
in most cases manages to print in angles between 30 and 45 degrees (yellow colour)
anything over 45 degrees will collapse


The ColorRamp can hold values from 0 to 1 while the Normal is 0 to 90 degrees.


Value 0 = 0 degrees
Value 1 = 90 degrees


As a result for this example:


Value 0.333 = 30 degrees
Value 0.5 = 45 degrees




See a nice comparison of how the self-support angle affects the 3D print (note that it is measured from horizontal surface rather than vertical direction in this photograph :/).